Field of the Invention
The present invention relates to a distributed control system for a vacuum sewer system in which sewage in a sump is sucked through a suction pipe by opening a vacuum valve and sent to a predetermined place, e.g., collection tank, and more particularly to apparatuses and methods for monitoring and controlling sewage transportation processes of a vacuum sewer system.
Background Art
FIG. 3 shows one example of the arrangement of a conventional vacuum sewer system which sewage 351 in a sump is sucked through a suction pipe by opening a vacuum valve and sent to a predetermined place. Reference numeral 350 denotes a sewage sump. One end of a suction pipe 310 is inserted into the sump 350. The other, or rear, end of the suction pipe 310 is connected to a sewage transport conduit 320 which communicates with a collection tank (vacuum system and tank not shown) through a vacuum valve 330. A vacuum valve body 331 has in a chamber 332 a diaphragm 333 and a spring 334 for biasing the diaphragm 333 into a valve closing position.
The vacuum valve 330 functions within this system by sealing and unsealing the passage between two parts of an evacuated system to define a vacuum valve cycle. The mechanical vacuum valve controller 390 functions within this system for open/close controlling the vacuum valve 330. The general structure and method of operation of this type of vacuum valve and controller is described in U.S. Pat. No. 5,588,458, issued to Ushitora, et al.
Reference numeral 390 denotes a controller for open/close controlling the vacuum valve 330. The controller 390 has a first input port connected through a pipe assembly 381 to a sump sensor tube 380, which is disposed in the sump 350. In addition, the controller 390 has a second input port connected through a pipe assembly 311 to a suction pipe 310, which is disposed in the sump 350. Further, the controller 390 has an outside air input port connected through a pipe assembly 391 to an outside air breather 392. Furthermore, the controller 390 has a valve output port connected through a pipe assembly 336 to the vacuum valve 330. Finally, the controller 390 has a vacuum source port connected through a pipe assembly 321 to the transport conduit 320.
In the vacuum sewer system arranged as shown in FIG. 3, when the level of sewage in the sump is low, and consequently the system is in a stand-by position, the lower end of the sensor tube lies above the sewage surface. No pressure is detected at the controller's sensor input port which signifies that no sewage is in sump, wherein the controller couples the outside air port to the valve output port. Since atmospheric pressure air through the air breather is communicated to the outside air port and therefore to the valve output port, the chamber 332 in the vacuum valve body 331 is placed under atmospheric pressure. Accordingly, the main valve 335 is pressed in the direction for closing the vacuum valve by the spring 334 and thus set in fully-closed state.
As the level of sewage in the sump rises, the pressure in the sump sensor tube rises. When the pressure in the sump sensor tube exceeds a water column of about 10 inches, the controller couples the vacuum in the transport conduit to the chamber in the vacuum valve body. Thus, the vacuum in the chamber overcomes the force of the spring and raises the main valve from its seat, thereby setting the vacuum valve in the fully-open state (i.e., a state where the bore that provides communication between the suction pipe and the transport conduit is open).
When the vacuum valve is set in the fully-open state, sewage in the sump is sucked up, and the sewage level begins to fall. The pressure in the sump sensor tube immediately drops, wherein the controller couples the atmospheric pressure air from the air breather into the chamber in the vacuum valve body causing the main valve to close.
In the vacuum sewer system arranged as shown in FIG. 4, an operational vacuum sewage system requires that each sewage inlet point, typically serving one or more houses, include a vacuum valve 430 and controller 490, which allows intermittent passage of accumulated sewage 451 into an associated transport conduit 420 network connected at the other end to a collection tank, and thereafter ultimately to a sewage treatment plant. As disclosed in U.S. Pat. No. 4,179,371, issued to B. E. Foreman et al., this transport conduit is typically laid with a saw-toothed profile with a combination of a riser conduit portion 421, low-point conduit portion 422, and down-slope conduit portion 423 (collectively called a “lift”) repeated throughout the length of the sewer main to accommodate the topography (e.g., other conduits and rock layers), as well as incoming flows from transport conduits leading to other individual vacuum valves. The slope of the down-slope conduit portions of the profile is such that the drop between lifts is generally equivalent to at least 40% of the conduit diameter (80% if the diameter is smaller than 6″) or 0.2% of the distance between lifts, whichever is greater. Generally, the transport conduit network is continuously maintained under vacuum or sub-atmospheric pressure. Sewage and air, usually at atmospheric pressure, are introduced for transport into the conduit through an open vacuum valve. The air moves down the length of the conduit to the area under vacuum or sub-atmospheric pressure where the air expands volumetrically. The energy created by the rapid movement of air in response to the differential pressure condition in the conduit in turn produces rapid sewage transport downstream throughout the conduit system. At a predetermined point in time, however, the vacuum valve will close, thereby ending the sewage transport cycle. The expansion of air causes a reduction in its pressure and velocity, and any residual waste not transported through the conduit network during the sewage transport cycle comes to rest. The conduit downstream of the vacuum valve is equalized by the source of vacuum pressure to a substantially constant sub-atmospheric or vacuum pressure condition throughout. Any residual waste not transported through the conduit during the sewage transport cycle will generally come to rest in the low point portion, permitting vacuum or sub-atmospheric pressure to be communicated upstream and maintained throughout the entire conduit section.
The conventional vacuum sewer system, arranged as described above, however, suffers from the following problems:
Vacuum sewers are a mechanized system of wastewater transport. Unlike gravity flow, vacuum sewers use differential air pressure to move the sewage. Sewer main lines are laid out in a sawtooth profile design so that the wastewater does not completely fill or “seal” the pipe bore. By doing this, air flows above the liquid and the vacuum that is created at the vacuum station can be transferred along the length of the vacuum sewer mains to every valve pit.
The vacuum produced by a vacuum station is generally capable of lifting 13 feet of sewage. Lift is achieved through a sawtooth layout of the lines consisting of two 45-degree fittings connected with a short length of pipe, creating a sawtooth “lift section”. Should the lift section be sealed for any reason, liquid is suspended on the downstream side of the lift and an associated vacuum loss is incurred. For every lift section filled with water, about 1 to 2 feet of lift is lost from the modest initial 13 feet of lift, leading to a waterlogged sewer main.
Culvert and utility crossings often dictate numerous variations in the burial depth of sewer mains, resulting in many sags and summits These sags and other poorly constructed sections are the weak points of a system and will be the first lift sections trapped with sewage when the system is stressed, e.g. during periods of high sewage surge flow or extremely low sewage flow. Monitoring the status of these weak points will indicate the overall health of the vacuum sewer system and provide the operator with a preemptive maintenance tool.
It's impossible to know if a lift section underground is waterlogged without the aid of monitoring equipment. However, a simple measurement of pressure drop across the lift section will indicate whether air or liquid is present in the lift section; and while simple in application, it is an otherwise impossible task without installed equipment. The present invention uses the transport conduit apparatus as a monitoring solution that simply measures the conditions of a lift section, and then uses a battery powered computer with wireless capabilities to wirelessly notify the operator of the status, e.g., a waterlogged lift section. There is no existing prior art to monitor the transport conduit conditions as achieved in this present invention.
At the end of the transport conduits are the valve pits which inject sewage in the transport conduits. The mechanical vacuum valve controller in the valve pit is solely a mechanical device with limited capabilities. Cost constraints prohibit the ability to build a solely mechanical vacuum valve controller with abilities to have the multiple sensor input ports and memory of past events, which are required for processing and calculating additional operating parameters, e.g., determining a partially open vacuum valve, calculating the air-to-liquid ratio, and summing sewage usage. The valve pit apparatus described in this invention will incorporate most all the mechanical valve controller features of prior art and incorporate the new features of this invention at an affordable cost for new and existing installations.
Vacuum valves will get stuck open or partially open due to many reasons including sewage solids getting caught in the valve seat. Further, sewer main lines connecting the valve pit to the vacuum station periodically get waterlogged and obstructed. Furthermore, water infiltration and inflow due to leaks and faulty connections will cause inefficient sewer system operations. Incorporating monitoring equipment to detect these theses adverse conditions is desirable. There is no existing prior art that will detect these conditions, in particular, by processing the measurements comprising, vacuum in the valve pit suction pipe and differential pressure across a riser conduit. Additionally, there is no existing art that can easily be retrofitted to existing installed valve pits or transport conduit sections to perform these tasks as mentioned.
A valve may be stuck partially open a small amount or a large amount, wherein knowing the amount the valve is open is important to the operator for determining whether immediate service is required. Prior art valve position sensors just determine if a valve is completely close, but not how much the valve is open. There is no existing prior art that will measure the amount the valve is open, record this condition and save in memory for later retrieval, nor report this condition to the operator for maintenance.
Vacuum sewer transport conduits will get blocked due to waterlogging during times of surge flow, which is indicated by a low vacuum in the transport conduit at the valve pit. Holding the sewage in the sump until the vacuum recovers to a suitable level will help prevent waterlogging the transport conduits during peak times or surge flow conditions, e.g., special community events or rain storms. Prior art designs evacuate the sump at a specific level and do not check for a vacuum level at the transport conduit. This invention will use the sump storage to hold the sewage until the transport conduit vacuum recovers. There is no existing prior art to detect this condition, make decisions based on the conditions, record this condition, save in memory for later retrieval, nor react to and report this condition to the operator for maintenance.
Vacuum sewer transport conduits will become waterlogged when not enough air and too much liquid are present in the conduit. Water hammering is a symptom of a waterlogged transport conduit. There is no existing prior art to detect this condition and attempt to automatically clear this condition by opening and closing a vacuum valve to admit additional air to a vacuum main.
Vacuum sewer systems operate inefficiently when water infiltration and inflow are present due to leaks and improper connections to storm water drains. There is no existing prior art to calculate the amount of sewage usage (amount of evacuated from the sump into the sewer system) per valve pit over a predetermined time period and uses the results for comparison to flow through a transport conduit to determine if there are leaks in the transport conduits. Nor is there existing art to use the sewage usage and flow measurements system-wide to determine the amount of water infiltration and inflow; thereby calculating the efficiency of the vacuum sewer system.
Vacuum sewer transport conduits operate efficiently when there is a proper air-liquid ratio, which is largely determined by the timing of the valve opening and closing time duration. There is no existing prior art to calculate the air flow time and liquid flow time, whereby allowing the calculation of air-to-liquid flow ratio and use this air-to-liquid flow ratio to control the closing of the vacuum valve after opening to evacuate the sump and allowing the proper amount of air to enter the transport conduit. The general explanation and importance of air-to-liquid ratio in a vacuum sewer system is described in U.S. Pat. No. 5,044,836, issued to Grooms. This invention controls the air-to-liquid ratio using real-time control algorithms to determine when enough air has been injected into the transport conduit and then closes the vacuum valve.
Monitoring of vacuum sewer transport conduits has been limited to a simple measurement of the gauge vacuum (reference to atmosphere) at a point in the transport conduit. There is no prior art to measure and calculate the air-to-liquid ratio in the transport conduit, monitor sewage flow through the transport conduit, detect a waterlogged situation in the transport conduit, nor detect water infiltration due to leaks in the transport conduit. The present invention measures sewage conditions in the transport conduit using differential pressure across the riser. This method does not need reference to atmospheric air pressure as in typical vacuum measurement techniques. Furthermore, by monitoring both the injection of sewage into the transport conduits at each valve pit and the flow through the transport conduits at points upstream, a central control computer can detect leaks in the transports conduits. There is no prior art that monitors the conditions in transport conduits, in particularly, measuring conditions by sensing the differential pressure across the riser and not needing reference to atmospheric air pressure as in this patent.
Monitoring of existing installed valve pit equipment comprising vacuum valves, suction pipes, and sensor tubes requires replacing or refurbishing the vacuum valve with a valve position sensor. The present invention can be installed and used without the valve position sensor installed, whereby saving cost. Furthermore, the present invention determines the valve position as open, partially open, or close and the degree of partially open. There is no prior art that allows monitoring the valve position without installation of a valve position sensor on the vacuum valve.
In view of the above-described circumstances, it is an object of the present invention to provide a valve pit apparatus for a vacuum sewer system, which is free from the above-described disadvantages and provides the above-described advantages which is capable of stably operating with a simplified structure. A further object of the invention is a wireless communications means of distributed control for the control and data collection of remote valve pits and transport conduits that is simple and economic to install and maintain. Furthermore, the valve pit apparatus, transport conduit apparatus, and distributed control system presented in this invention is straight forward, simple, affordable, and able to be installed on existing installed valve pits and transport conduits with little labor effort.